1. Field of the Invention
The present invention is related to a thin film transistor array, a method for manufacturing the thin film transistor array and an active matrix display.
In addition, the present invention is related to a thin film transistor array, a method for manufacturing the thin film transistor array and an active matrix display, the transistor being able to be used for a driving device of various image display devices, a logic device of various logic circuits or the like.
2. Description of the Related Art
According to a remarkable development of the information technology, now, information is frequently sent or received using a mobile information terminal, a notebook computer and the like. It is well-known that, in near future, the ubiquitous society will be realized so that information is sent or received at any place. In such a society, a thinner and lighter information terminal is desired.
Now, main stream of the semiconductor material is silicon type (Si type). However, the research and development of the transistor using an organic semiconductor (the organic transistor) have become active in views of improving the flexibility, reducing the weight and reducing the cost. In the case of the organic semiconductor, process in wet state can be generally adopted. Therefore, there are some advantages of the organic semiconductor. For example, increasing the size is possible, a printing method can be adopted and a plastic substrate can be used. (See non-patent document 1.)
In addition, the application field of the organic semiconductor is wide, and is not limited to the above-mentioned thin, light and flexible display. The application of the organic semiconductor to RFID (radio frequency identification) tag or a sensor is expected. In this way, for the ubiquitous society, the research and development of the organic transistor is necessary.
From these reasons, now, the research and development of the organic semiconductor using a printing method gather attention.
On the other hand, an amorphous oxide semiconductor InGaZnO4 was published in Patent Document 1. InGaZnO4 can be formed at a room temperature, and electric field mobility of InGaZnO4 is more than amorphous silicon. InGaZnO4 may be used as an oxide semiconductor. It is expected that InGaZnO4 is a material for a high performance flexible transistor.
In addition, it is necessary for a sealing layer to be formed over a semiconductor since the characteristics of the semiconductor deteriorates due to oxygen or water entering the semiconductor.
Especially, characteristics of an organic semiconductor tend easily to change due to oxygen or water compared with an inorganic material. Therefore, a role of a sealing layer is important.
In addition, in the case where a semiconductor of an oxide is used, a role of a sealing layer is important in order to improve the characteristics.
An inorganic insulating layer, for example, silicon oxide and silicon nitride, is used for a sealing layer of an electric field effect type thin film transistor using a semiconductor having a main component of the above-mentioned oxide.
Further, patterning of the above-mentioned sealing layer is performed by a liftoff method or an etching method by which microfabrication is generally possible.
However, in the case of a thin film transistor array, if a sealing layer is formed as a dot-shaped pattern on respective thin film transistors, alignment accuracy is poor. Therefore, the transistor is easily influenced by oxygen etc. Thereby, there are problems in that characteristics degradations easily occur. For example, mobility of a semiconductor becomes small and ON/OFF ratio becomes small.
In addition, when a dot-shaped sealing layer is formed, there are the following problems: when a thin film transistor array is two-dimensionally observed from an upper part, misalignment of respective dots in both directions of X-axis and Y-axis occurs; thereby, it is difficult to keep alignment accuracy; and yield is low.
In addition, in the case where patterning of a sealing layer is performed by a liftoff method so that a sealing layer pattern comprised of an isolated pattern of a small dot is formed, a resist is applied the entire part except for the isolated pattern of the small dot. Therefore, there is problem in which the resist is difficult to be peeled off, thereby the processing time becomes long and the yield becomes small.
In addition, in the case where patterning is performed by an etching method, for example, a dry etching method using a fluorine system gas such as carbon tetrafluoride, a wet etching method using fluorinated acid are used. However, in the case of an isolated pattern of a small dot, etching characteristics are difficult to be controlled, thereby there is a problem in which the yield becomes small.
The present invention is made by considering these problems. One object of the present invention is to provide a thin film transistor array in which characteristics degradation is inhibited.
In addition, another object of the present invention is to provide a method for manufacturing a thin film transistor array in which a sealing layer can be formed while the alignment accuracy is good and the yield is high.
Further, another object of the present invention is to provide an active matrix display in which a high quality image display is possible by stabilizing characteristics of a semiconductor.    [Non-Patent Document 1] Science Vol. 265, 1684(1994)    [Patent Document 1] JP-A-2006-165532